In recent years, development of higher definition CCD/CMOS image sensors is underway, and this requires the improvement in sensitivity of the sensors. Therefore, microlenses mounted on such sensors are required to have high transparency and high heat resistance.
A known method for producing a microlens for CCD/CMOS image sensors is an etch back method (Patent Document 1 and Patent Document 2). That is, a resist pattern is formed on a resin layer for a microlens formed on a color filter layer, and this resist pattern is heat-treated to cause reflow, thus forming a lens pattern. The lens pattern formed by allowing this resist pattern to reflow is used as an etching mask, and the resin layer for a microlens as the underlayer is subjected to etch back to transfer the lens pattern shape to the resin layer for a microlens. Thus, a microlens is produced.
In the etch back method, in order to transfer a lens pattern shape accurately to a resin layer for a microlens as the underlayer, it is required that the dry etching rate X of the resist and the dry etching rate Y of the resin layer for a microlens be substantially equal. In many cases, a resin containing a novolac resin is used as the resist. However, depending on the shape of the microlens and the evaluation environment, it may be required that the dry etching rate Y of the resin layer for a microlens be 1.3 times to 1.7 times the dry etching rate X of the resist containing a novolac resin (X:Y=1:1.3 to 1.7). Examples of such a case include a case in which a resist containing an acrylic resin, which has a larger dry etching rate than a resist containing a novolac resin, is used as the resist.